We’re all different, and, as such, there are no real absolutes in training. So when discussing best practices, it’s always important to keep that in mind. That said, there is research that backs up and provides answers to certain important questions. Like, what is the best time of day to train to maximize muscle growth?
In an issue of the International Journal of Sports Medicine, researchers examined peak strength at four different times of the day (7 a.m.-8 a.m., 12 p.m.-1 p.m., 5 p.m.-6 p.m., 10:30 p.m.-11:30 p.m.) for two consecutive days. The researchers reported that the morning values were significantly lower when compared to the rest of the day. There are many variables which can affect a lifter’s ability to generate peak force; however, none of the variables measured (sleep, stress level, normal circadian rhythms of the person, morning or night person) had a significant effect on the outcome. This study was similar to an earlier study, which had subjects perform peak isometric strength parameters from 8 a.m.-9 a.m., 1 p.m.-2 p.m. and 6 p.m.-7 p.m.; peak strength was greatest between 6 p.m.-7 p.m. When they compared the percent increase from session to session, there was a 2.76 percent increase from the morning to afternoon session, but only an 11.13 percent increase from the afternoon to the evening session.5
Similar results were also reported in the Journal of Electromyography and Kinesiology. Researchers found that peak muscle strength was higher at 6 p.m. compared to 6 a.m.4 The average increase in strength from morning to evening was 4.6 percent. Clearly, this is not a psychological issue, yet more of a physiological condition. This is not the first study to demonstrate this effect; at least two other studies have demonstrated peak strength to be higher at 6 p.m. than at 6 a.m.2, 3 This means that much like there are changes in GH/cortisol throughout the day, there are also circadian rhythms in strength during the day, with strength being higher in the afternoon/early evening.
Temperature And Muscle Strength
So why is muscle strength higher in the afternoon compared to the morning? There is one physiological variable that seems to correlate with the peak increases in strength: body temperature. Body temperature is lowest in the morning and increases throughout the day. Muscular strength and body temperature appear to be associated by some researchers.6, 7 It is now recognized that torque and temperature vary during the day, but fluctuations in torque cannot be entirely explained by change in temperature. Maximal performance is generally improved by the end of the afternoon, at the peak of the body temperature curve.7, 8 Some studies have suggested that the simultaneous increases in both body temperature and muscular performance are causally related, and that the circadian rhythm of body temperature could be regarded as a passive warm-up effect.9
Why Temperature Is Important
The change in body temperature seems to have a favorable effect on increasing strength. In a previous study conducted in a tropical environment, researchers failed to show any daytime variation in muscle performance. That suggests that the passive warm-up effect of the moderately warm and humid environment may have blunted the passive warm-up effect of time of day.10 Researchers from France did a study in which they manipulated the temperature at various times of the day. The following four sessions were conducted in random order, in the following conditions: morning/neutral; morning/moderately warm and humid; afternoon/neutral; afternoon/moderately warm and humid. The results of the study suggest that muscle contractility was differently influenced by a moderately warm and humid exposure, depending on whether the tests were performed in the morning or in the afternoon. That is, depending on the initial level of body temperature. For example, in the morning, muscle contraction was significantly increased in moderately warm and humid conditions in comparison with neutral environment, whereas it did not vary in the late afternoon, which explains the lack of variation in maximal contractions in the moderately warm and humid conditions.
This shows that muscle force was more sensitive to an external passive warm-up effect in the morning, when body temperatures are at their lowest levels. Nevertheless, muscle force does not seem to be sensitive to an external passive warm-up effect in the afternoon, when body temperatures are at their highest levels. In summary, the data showed that both a warm exposure and the diurnal increase in body temperature influence muscle contractility to increase muscle strength, but that the improvement in muscle contractility after these two passive warm-ups cannot be combined to improve force to a greater level. This suggests that a ceiling effect of the possible beneficial effects of passive warm-ups is reached with either the diurnal increase in body temperature or a moderately warm exposure.
Temperature Theories
Researchers are not sure how muscle temperature affects muscle strength, but some interesting theories have been suggested. The increases in afternoon strength do not seem to be mediated by the nervous system, but most likely are mediated at the peripheral level (muscle itself).14 One theory suggests greater Ca2 retention by the sarcoplasmic reticulum (Ca, which causes muscle contraction, is stored in the sarcoplasmic reticulum) decreases when the temperature drops.12, 13 Another possibility is that interleukin-6, tumor necrosis factor and cortisol all have diurnal variations, which are higher in the morning compared to the afternoon. Blood flow to muscle could also be a contributing factor.
British researchers looked at heart rate, core temperature, sternum skin temperature and forearm skin blood flow during exercise, and throughout a subsequent 30-minute recovery period in 12 males exercising at 70 percent VO2max at both 8 a.m. and 6 p.m. Comparisons were made of the changes of heart rate, temperature and skin blood flow produced by the exercise at the two times of day. What the researchers found was that the increases in core and sternum temperatures during the afternoon exercise were significantly less than the morning, even though the workloads were not significantly different. Also, resting forearm skin blood flow (a measure of the ability of the body to lose excess heat) was higher in the afternoon exercise bout and the rate of change of blood flow as exercise was commenced was also higher.
What If You Can Only Train In The Morning?
If you can only train in the morning, are you totally screwed? Most of the studies examining strength changes in the morning and afternoon have used participants who normally train in the afternoon, which cloud the results of the study. Previous research has documented that several weeks of repeated strength training performed in the morning hours may reduce the typical diurnal strength patterns by increasing maximum strength more in the morning than at other times of day.17 This means that after several weeks of training in the morning, the body resets the nervous system to adapt to morning strength sessions.
In fact, a previous study reported that traditional low-frequency strength training performed in the morning, but not in the afternoon, was found to attenuate the typical diurnal variation in maximum strength. However, the absolute increase in maximum strength was similar regardless of the time of day of training.18 It seems that if you normally train in the afternoon, maxing out in the morning is going to lead to a reduction in peak strength, but after several weeks of morning training, the body adapts.
In conclusion, getting to the gym at the same time of day on a consistent basis is the key point, regardless of whether it’s in the morning or afternoon. It seems that there are circadian rhythms in strength during the day, with peak strength peaking in the afternoon compared to the morning. Many studies have demonstrated that peak strength is casually related with body core temperature. Muscle temperature can explain some, but not all the variations in muscle strength throughout the day. If you have to train in the morning, you can also increase muscle strength by raising body temperature.
You may want to bundle up and get a good sweat going before starting to work out. As the study mentioned earlier, lifters were able to increase muscle strength in the morning when they trained in a warm/humid environment. Sitting in a sauna for 15 minutes before training or spending a little extra time warming up may be needed to increase body core temperature. If you have to max out at a certain time of the day, try to schedule an afternoon session, which seems to be when peak strength hours occur. It also seems that training in the morning for several weeks causes the body to adapt to morning training, which can favor strength increases.
References:
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